audioclip stream has delay

I have set up a audiosource playing a streamed audioclip which is being set using the PCMReaderCallback. It is playing the audio correctly except from it having a 1 second delay.
I have it being created with the following parameters

I have tried increasing and decreasing the “lenghtSamples” but it seams to have had no effect.

I am setting the data to values stored in a buffer which are used as soon as they are available in OnReaderCallback.

Can someone please tell me if I am missing something which is causing the delay or if it is just the buffer is a second behind the source?

The lag is introduced during the start, then everything will be 1 second delay, but the sound is smooth